Should i get a color or b/w print for proofing my work?

Im a freelance graphic designer, most of my works includes, visual identity, posters, flyers, and almost everything printed work. Usually i just send an email JPEG sample, but now a i'been asked to design a magazine. In the first 2 editions i had trouble with the client for some "errors" so now i want them to sign a "dummy" printed magazine, something to cover myself. But i dont know for how long im gonna be doing this magazine. On the other hand always giving a printed sample is going to give me a more professional look? besides i could hand over my stimates, invoice printed, so 2 questions here, should i get a printer? wich one, color or b/w?. Thnxs for read and answer!